In a conventional apparatus of this type, a pulse-width modulated signal according to an image density is formed, and a laser is caused to emit light on the basis of the pulse-width modulated signal, thereby forming a dot latent image on a photosensitive drum.
However, if transmission or drive lines among a circuit for generating the pulse-width modulated signal, a laser driver, and a laser diode are long, a halftone pattern cannot be satisfactorily reproduced.
More specifically, a laser ON time for a low-density portion of a halftone portion is, e.g., 5 nsec, and ultra-high-speed driving must be performed. In a conventional circuit, when a semiconductor laser is driven, since a pulse signal must be transmitted to a semiconductor laser element over a certain distance, the waveform of the pulse signal is distorted, and small pulses are made unstable. As a result, the laser cannot accurately emit light.